1. Field of the Invention
The present invention generally relates to devices and methods for applying and/or drying a coating material, and particularly relates to a device and a method for applying a coating material to and/or drying a coating material on printed-circuit boards or plates of sheet-metal work.
2. Description of the Related Art
An increasing demand for low-cost printed-circuit boards which are miniaturized in multiple thin layers and high-density wiring patterns calls for methods which can form low-cost and high-quality circuits with high precision.
In the field of sheet-metal work, also, methods which can achieve high precision while incurring low costs are demanded. Thus, a chemical milling method which can form complex patterns at fast speed has been increasingly used.
A method of putting dry films on printed-circuit boards to form circuits incurs high costs. Also, a device for putting the dry films on the printed-circuit boards must be stopped when replenishing the dry films, thereby disturbing a flow of a manufacturing line. On the other hand, a method of applying liquid photosensitizer to printed-circuit boards incurs relatively low costs, and there is no need to stop a device when replenishing the photosensitizer. Thus, it is preferable to use the liquid photosensitizer for printed-circuit boards.
In order to produce printed-circuit boards with high precision, a photosensitizer which is highly sensitive and yet stable is required. When a highly sensitive photosensitizer is used, however, applying he photosensitizer to each surface of a printed-circuit board consecutively results in a photosensitizer on one surface being exposed to more heat in a drying process than a photosensitizer on the other surface. Thus, a difference in a sensitivity of the photosensitizer will develop between the two surfaces. Because of this, it is preferable to apply photosensitizer to both surfaces simultaneously, which is also preferable for a process-time reduction. Also, installing one device for applying and drying a coating material for both surfaces requires less investment than installing two devices for only one surface and connecting the two devices in a series. Thus, it is preferable to use a device for applying a coating material to both surfaces simultaneously.
When various types of printed-circuit boards are manufactured in a small quantity, a direct-drawing method is often used, instead of using a number of master films corresponding to these various types. The direct-drawing method uses a laser beam directly controlled by a CAD (computer-aided design) system. The direct-drawing method is suited to manufacturing of products of various types, and can speed up the entire production process. The direct-drawing method uses a high-sensitivity photosensitizer so that an applying process must be conducted in a darkroom.
In the chemical milling method used for a low-cost and high-precision metal-sheet work, a coating material (photosensitizer) is required to be applied to both surfaces simultaneously as in the case of the printed-circuit boards.
In the related art, a method employing rolls is used to apply photosensitizers to both surfaces. In this method, a photosensitizer is provided on a cylindrical roll having a surface of a resin type, and the cylindrical roll is rolled on a surface of a place to apply the photosensitizer to the plate.
In the method using the rolls of the related art, however, a coating material is applied to the entirety of both plate surfaces, thus providing no space to hold the plate when the coated plate is conveyed. Thus, human hands are required which are pushed against side edges of a plate to hold and carry the plate to a drying machine. In this method, however, an automation of the manufacturing process cannot be achieved, thus resulting in an inefficiency. When plates are conveyed by holding edges of the plates through a V-shape fixture, a conveyer, or the like, a coating material is bound to attach to these conveying devices. When a coating material is accumulated on surfaces of these conveying devices, the accumulated coating material might damage the coated surface of the plates. Also, such accumulation may result in a malfunction of the applying device or the drying device.
In the method using the rolls of the related art, a solution concentration of a coating material is increased when the coating material needs to be applied thicker. However, a thicker coating material is more likely to develop cracks. Also, when a thick coating material on both surfaces of a plate is dried, the coating material on either surface may be affected by gravity to develop draping of the coating material. Thus, applying a thick coating material makes it difficult to obtain a coated surface of a good condition.
Also, related-art devices using the rolls have a structure such that rolls for applying a coating material are difficult to be exchanged. When these rolls need to be exchanged because of defects or wearing, a manufacturing line must be stopped for a long time. When these rolls are cleaned by rolling them, chances of having an accident such as getting hands caught in the rolls cannot be eliminated.
Also, as the related-art devices for applying a coating material do not have light shields, a room where the devices are installed should be turned into a darkroom. This leads to an increase in investment, and makes it difficult to move the facility.
Also, when a solder resist is applied or a build-up method is used, it is necessary to apply an insulating resin or a photosensitizer to an irregular surface of a previously formed circuit. The related-art devices which use rolls having a relatively hard surface made of a vinyl type, a polyurethane type, or the like are suited to an application of a coating material to a flat plate, but are not suited to an application of a coating material to an irregular surface. When a hard surface of rolls of the related-art devices is used, an applied coating material becomes thin on peaks of the surface, and becomes thick in valleys of the surface.
Stabilization of the sensitivity of a photosensitizer requires the control of the thickness of a coating material. In the related-art devices, the control of the concentration of a coating material is conducted by adjusting a pressure of the rolls pushed against the plates or by adjusting the amount of a solution and a photosensitizer based on the measurement of the thickness of an applied coating material after it is dried. As noted before, an applied coating material becomes thicker as the concentration of the coating material becomes higher. In these devices, however, a continuous control of the thickness cannot be achieved so that it is difficult to obtain a constant thickness.
With regard to a drying process of a coating material, the problems are as follows. Related-art methods of drying a coating material applied to both surfaces of plates include a method of drying the coating material while conveying the plates by using the V-shape fixture, and a method of drying the coating material while conveying the plates by hanging the plates with clamps. The method of drying a coating material while conveying plates by using the V-shape fixture cannot eliminate a possibility that the plates bend to touch the V-shape fixture when thin plates are used. Here, thin plates are often used for forming circuits of inner layers.
In the method of drying the coating material by hanging the plates, the plates bend due to a difference in thermal expansion coefficients between the plate and the coating material. When bending is developed, a distance between the plates and a heat source is changed so as to bring about an irregularity in the dryness of the coating material. Also, a process of correcting the bending is required at a later stage. In this method, when plates of a regular shape and size are used, these plates can be set to an operating position for hanging the plates automatically. However, when plates of an irregular shape and size are used, human hands are required to set the plates to the operating position.
Accordingly, there is a need for a method and a device for applying a coating material which can apply the coating material to both surfaces of plates except for a holding area provided on the surfaces so as to enable the plates to be easily conveyed.
Also, there is a need for a method and a device for applying a coating material which can apply the coating material in a constant thickness through a continuous control of the thickness.
Furthermore, there is a need for a method and a device for drying a coating material which do not bring about the bending of plates.